Abstract
The level of tungstate in freshwater is disturbing due to its toxicity and its impact to human health. Thus, the current study explores the use of Ag nanoparticle (AgNP)-treated activated carbon (AgNPs/AC) nanocomposite as solid phase extractor (SPE) for removal of trace levels of tungstate ions in water. The AgNPs/AC was synthesized by chemical binding of Ag nanoparticles onto AC. The microstructure image indicated that the AgNPs were uniformly dispersed on AC surface and thus maintaining high surface area. Scanning electron micrographs of AgNPs/AC revealed a three-dimensional structure which is suitable as SPE. The AgNPs/AC nanocomposite was used as a low-cost and effective SPE for tungstate removal from water. Adsorption of tungstate from aqueous media reached maximum at pH approximate to 4 and reached equilibrium in <20 min. Tungstate sorption followed pseudo-second-order kinetic with an overall rate constant (k) of 0.72 min.(-1) The negative values of H and Delta G are interpreted as exothermic and spontaneous reaction of tungstate sorption by the adsorbent, respectively. The positive value of Delta S (R-2=0.999) reflected good absorption and/or adsorption of the oxyanion [WO4](2-) as an ion associate with the bulky cations and the surface area available in the nanocomposite. The sorbent AgNPs/AC was also packed column for preconcentration of trace levels of tungstate in tap water samples. Tungstate species were satisfactorily recovered with NaOH (1.0 mol L-1) and subsequently ICP-OES analyzed.